--> ABCL:       ((,) . PI)
 --> Allegro:    (BQ-COMMA PI)
 --> CCL:        (`, . PI)

 --> Clasp:      (UNQUOTE PI)
 --> CLisp:      

ERROR: READ: unquotes may not occur in arrays

 --> CMUCL:      ((,) . PI)
 --> ECL:        (UNQUOTE PI)
 --> SBCL:       ERROR: READ error during LOAD:

         Comma inside a backquoted array (not a list or general vector.)

           Line: 2, Column: 13

           Stream: #<SB-INT:FORM-TRACKING-STREAM for "file /tmp/cl-all.lisp" {10036C6EE3}>